HTTP Utilities — Werkzeug Documentation (3.1.x)

# HTTP Utilities

Werkzeug provides a couple of functions to parse and generate HTTP headers that are useful when implementing WSGI middlewares or whenever you are operating on a lower level layer. All this functionality is also exposed from request and response objects.

## Datetime Functions

These functions simplify working with times in an HTTP context. Werkzeug produces timezone-aware `datetime` objects in UTC. When passing datetime objects to Werkzeug, it assumes any naive datetime is in UTC.

When comparing datetime values from Werkzeug, your own datetime objects must also be timezone-aware, or you must make the values from Werkzeug naive.

- `dt = datetime.now(timezone.utc)` gets the current time in UTC.

- `dt = datetime(..., tzinfo=timezone.utc)` creates a time in UTC.

- `dt = dt.replace(tzinfo=timezone.utc)` makes a naive object aware by assuming it’s in UTC.

- `dt = dt.replace(tzinfo=None)` makes an aware object naive.

werkzeug.http.parse_date(value)

  Parse an RFC 2822 date into a timezone-aware `datetime.datetime` object, or `None` if parsing fails.

  This is a wrapper for `email.utils.parsedate_to_datetime()`. It returns `None` if parsing fails instead of raising an exception, and always returns a timezone-aware datetime object. If the string doesn’t have timezone information, it is assumed to be UTC.

  Parameters:

    value (str | None) – A string with a supported date format.

  Return type:

    datetime | None

  Changelog

  Changed in version 2.0: Return a timezone-aware datetime object. Use `email.utils.parsedate_to_datetime`.

werkzeug.http.http_date(timestamp=None)

  Format a datetime object or timestamp into an RFC 2822 date string.

  This is a wrapper for `email.utils.format_datetime()`. It assumes naive datetime objects are in UTC instead of raising an exception.

  Parameters:

    timestamp (datetime | date | int | float | struct_time | None) – The datetime or timestamp to format. Defaults to the current time.

  Return type:

    str

  Changelog

  Changed in version 2.0: Use `email.utils.format_datetime`. Accept `date` objects.

## Header Parsing

The following functions can be used to parse incoming HTTP headers. Because Python does not provide data structures with the semantics required by RFC 2616, Werkzeug implements some custom data structures that are documented separately.

werkzeug.http.parse_options_header(value)

  Parse a header that consists of a value with `key=value` parameters separated by semicolons `;`. For example, the `Content-Type` header.

      parse_options_header("text/html; charset=UTF-8")
      ('text/html', {'charset': 'UTF-8'})

      parse_options_header("")
      ("", {})

  This is the reverse of `dump_options_header()`.

  This parses valid parameter parts as described in RFC 9110. Invalid parts are skipped.

  This handles continuations and charsets as described in RFC 2231, although not as strictly as the RFC. Only ASCII, UTF-8, and ISO-8859-1 charsets are accepted, otherwise the value remains quoted.

  Clients may not be consistent in how they handle a quote character within a quoted value. The HTML Standard replaces it with `%22` in multipart form data. RFC 9110 uses backslash escapes in HTTP headers. Both are decoded to the `"` character.

  Clients may not be consistent in how they handle non-ASCII characters. HTML documents must declare `<meta charset=UTF-8>`, otherwise browsers may replace with HTML character references, which can be decoded using `html.unescape()`.

  Parameters:

    value (str | None) – The header value to parse.

  Returns:

    `(value, options)`, where `options` is a dict

  Return type:

    tuple[str, dict[str, str]]

  Changelog

  Changed in version 2.3: Invalid parts, such as keys with no value, quoted keys, and incorrectly quoted values, are discarded instead of treating as `None`.

  Changed in version 2.3: Only ASCII, UTF-8, and ISO-8859-1 are accepted for charset values.

  Changed in version 2.3: Escaped quotes in quoted values, like `%22` and `\"`, are handled.

  Changed in version 2.2: Option names are always converted to lowercase.

  Changed in version 2.2: The `multiple` parameter was removed.

  Changed in version 0.15: RFC 2231 parameter continuations are handled.

  Added in version 0.5.

werkzeug.http.parse_set_header(value, on_update=None)

  Parse a set-like header and return a `HeaderSet` object:

      >>> hs = parse_set_header('token, "quoted value"')

  The return value is an object that treats the items case-insensitively and keeps the order of the items:

      >>> 'TOKEN' in hs
      True
      >>> hs.index('quoted value')
      1
      >>> hs
      HeaderSet(['token', 'quoted value'])

  To create a header from the `HeaderSet` again, use the `dump_header()` function.

  Parameters:

    - value (str | None) – a set header to be parsed.

    - on_update (Callable[[HeaderSet], None] | None) – an optional callable that is called every time a value on the `HeaderSet` object is changed.

  Returns:

    a `HeaderSet`

  Return type:

    HeaderSet

werkzeug.http.parse_list_header(value)

  Parse a header value that consists of a list of comma separated items according to RFC 9110.

  This extends `urllib.request.parse_http_list()` to remove surrounding quotes from values.

      parse_list_header('token, "quoted value"')
      ['token', 'quoted value']

  This is the reverse of `dump_header()`.

  Parameters:

    value (str) – The header value to parse.

  Return type:

    list[str]

werkzeug.http.parse_dict_header(value)

  Parse a list header using `parse_list_header()`, then parse each item as a `key=value` pair.

      parse_dict_header('a=b, c="d, e", f')
      {"a": "b", "c": "d, e", "f": None}

  This is the reverse of `dump_header()`.

  If a key does not have a value, it is `None`.

  This handles charsets for values as described in RFC 2231. Only ASCII, UTF-8, and ISO-8859-1 charsets are accepted, otherwise the value remains quoted.

  Parameters:

    value (str) – The header value to parse.

  Return type:

    dict[str, str | None]

  Changelog

  Changed in version 3.0: Passing bytes is not supported.

  Changed in version 3.0: The `cls` argument is removed.

  Changed in version 2.3: Added support for `key*=charset''value` encoded items.

  Changed in version 0.9: The `cls` argument was added.

werkzeug.http.parse_accept_header(value: str | None) → Accept
werkzeug.http.parse_accept_header(value: str | None, cls: type[_TAnyAccept]) → _TAnyAccept

  Parse an `Accept` header according to RFC 9110.

  Returns an `Accept` instance, which can sort and inspect items based on their quality parameter. When parsing `Accept-Charset`, `Accept-Encoding`, or `Accept-Language`, pass the appropriate `Accept` subclass.

  Parameters:

    - value (str | None) – The header value to parse.

    - cls (type[_TAnyAccept] | None) – The `Accept` class to wrap the result in.

  Returns:

    An instance of `cls`.

  Return type:

    _TAnyAccept

  Changelog

  Changed in version 2.3: Parse according to RFC 9110. Items with invalid `q` values are skipped.

werkzeug.http.parse_cache_control_header(value: str | None, on_update: Callable[[_CacheControl], None] | None = None) → RequestCacheControl
werkzeug.http.parse_cache_control_header(value: str | None, on_update: Callable[[_CacheControl], None] | None = None, cls: type[_TAnyCC] = None) → _TAnyCC

  Parse a cache control header. The RFC differs between response and request cache control, this method does not. It’s your responsibility to not use the wrong control statements.

  Changelog

  Added in version 0.5: The `cls` was added. If not specified an immutable `RequestCacheControl` is returned.

  Parameters:

    - value (str | None) – a cache control header to be parsed.

    - on_update (Callable[[_CacheControl], None] | None) – an optional callable that is called every time a value on the `CacheControl` object is changed.

    - cls (type[_TAnyCC] | None) – the class for the returned object. By default `RequestCacheControl` is used.

  Returns:

    a `cls` object.

  Return type:

    _TAnyCC

werkzeug.http.parse_if_range_header(value)

  Parses an if-range header which can be an etag or a date. Returns a `IfRange` object.

  Changelog

  Changed in version 2.0: If the value represents a datetime, it is timezone-aware.

  Added in version 0.7.

  Parameters:

    value (str | None)

  Return type:

    IfRange

werkzeug.http.parse_range_header(value, make_inclusive=True)

  Parses a range header into a `Range` object. If the header is missing or malformed `None` is returned. `ranges` is a list of `(start, stop)` tuples where the ranges are non-inclusive.

  Changelog

  Added in version 0.7.

  Parameters:

    - value (str | None)

    - make_inclusive (bool)

  Return type:

    Range | None

werkzeug.http.parse_content_range_header(value, on_update=None)

  Parses a range header into a `ContentRange` object or `None` if parsing is not possible.

  Changelog

  Added in version 0.7.

  Parameters:

    - value (str | None) – a content range header to be parsed.

    - on_update (Callable[[ContentRange], None] | None) – an optional callable that is called every time a value on the `ContentRange` object is changed.

  Return type:

    ContentRange | None

## Header Utilities

The following utilities operate on HTTP headers well but do not parse them. They are useful if you’re dealing with conditional responses or if you want to proxy arbitrary requests but want to remove WSGI-unsupported hop-by-hop headers. Also there is a function to create HTTP header strings from the parsed data.

werkzeug.http.is_entity_header(header)

  Check if a header is an entity header.

  Changelog

  Added in version 0.5.

  Parameters:

    header (str) – the header to test.

  Returns:

    `True` if it’s an entity header, `False` otherwise.

  Return type:

    bool

werkzeug.http.is_hop_by_hop_header(header)

  Check if a header is an HTTP/1.1 “Hop-by-Hop” header.

  Changelog

  Added in version 0.5.

  Parameters:

    header (str) – the header to test.

  Returns:

    `True` if it’s an HTTP/1.1 “Hop-by-Hop” header, `False` otherwise.

  Return type:

    bool

werkzeug.http.remove_entity_headers(headers, allowed=('expires', 'content-location'))

  Remove all entity headers from a list or `Headers` object. This operation works in-place. `Expires` and `Content-Location` headers are by default not removed. The reason for this is RFC 2616 section 10.3.5 which specifies some entity headers that should be sent.

  Changelog

  Changed in version 0.5: added `allowed` parameter.

  Parameters:

    - headers (Headers | list[tuple[str, str]]) – a list or `Headers` object.

    - allowed (Iterable[str]) – a list of headers that should still be allowed even though they are entity headers.

  Return type:

    None

werkzeug.http.remove_hop_by_hop_headers(headers)

  Remove all HTTP/1.1 “Hop-by-Hop” headers from a list or `Headers` object. This operation works in-place.

  Changelog

  Added in version 0.5.

  Parameters:

    headers (Headers | list[tuple[str, str]]) – a list or `Headers` object.

  Return type:

    None

werkzeug.http.is_byte_range_valid(start, stop, length)

  Checks if a given byte content range is valid for the given length.

  Changelog

  Added in version 0.7.

  Parameters:

    - start (int | None)

    - stop (int | None)

    - length (int | None)

  Return type:

    bool

werkzeug.http.quote_header_value(value, allow_token=True)

  Add double quotes around a header value. If the header contains only ASCII token characters, it will be returned unchanged. If the header contains `"` or `\` characters, they will be escaped with an additional `\` character.

  This is the reverse of `unquote_header_value()`.

  Parameters:

    - value (Any) – The value to quote. Will be converted to a string.

    - allow_token (bool) – Disable to quote the value even if it only has token characters.

  Return type:

    str

  Changelog

  Changed in version 3.0: Passing bytes is not supported.

  Changed in version 3.0: The `extra_chars` parameter is removed.

  Changed in version 2.3: The value is quoted if it is the empty string.

  Added in version 0.5.

werkzeug.http.unquote_header_value(value)

  Remove double quotes and decode slash-escaped `"` and `\` characters in a header value.

  This is the reverse of `quote_header_value()`.

  Parameters:

    value (str) – The header value to unquote.

  Return type:

    str

  Changelog

  Changed in version 3.0: The `is_filename` parameter is removed.

werkzeug.http.dump_header(iterable)

  Produce a header value from a list of items or `key=value` pairs, separated by commas `,`.

  This is the reverse of `parse_list_header()`, `parse_dict_header()`, and `parse_set_header()`.

  If a value contains non-token characters, it will be quoted.

  If a value is `None`, the key is output alone.

  In some keys for some headers, a UTF-8 value can be encoded using a special `key*=UTF-8''value` form, where `value` is percent encoded. This function will not produce that format automatically, but if a given key ends with an asterisk `*`, the value is assumed to have that form and will not be quoted further.

      dump_header(["foo", "bar baz"])
      'foo, "bar baz"'

      dump_header({"foo": "bar baz"})
      'foo="bar baz"'

  Parameters:

    iterable (dict[str, Any] | Iterable[Any]) – The items to create a header from.

  Return type:

    str

  Changelog

  Changed in version 3.0: The `allow_token` parameter is removed.

  Changed in version 2.2.3: If a key ends with `*`, its value will not be quoted.

## Cookies

werkzeug.http.parse_cookie(header, cls=None)

  Parse a cookie from a string or WSGI environ.

  The same key can be provided multiple times, the values are stored in-order. The default `MultiDict` will have the first value first, and all values can be retrieved with `MultiDict.getlist()`.

  Parameters:

    - header (WSGIEnvironment | str | None) – The cookie header as a string, or a WSGI environ dict with a `HTTP_COOKIE` key.

    - cls (type[ds.MultiDict[str, str]] | None) – A dict-like class to store the parsed cookies in. Defaults to `MultiDict`.

  Return type:

    ds.MultiDict[str, str]

  Changelog

  Changed in version 3.0: Passing bytes, and the `charset` and `errors` parameters, were removed.

  Changed in version 1.0: Returns a `MultiDict` instead of a `TypeConversionDict`.

  Changed in version 0.5: Returns a `TypeConversionDict` instead of a regular dict. The `cls` parameter was added.

werkzeug.http.dump_cookie(key, value='', max_age=None, expires=None, path='/', domain=None, secure=False, httponly=False, sync_expires=True, max_size=4093, samesite=None, partitioned=False)

  Create a Set-Cookie header without the `Set-Cookie` prefix.

  The return value is usually restricted to ascii as the vast majority of values are properly escaped, but that is no guarantee. It’s tunneled through latin1 as required by PEP 3333.

  The return value is not ASCII safe if the key contains unicode characters. This is technically against the specification but happens in the wild. It’s strongly recommended to not use non-ASCII values for the keys.

  Parameters:

    - max_age (timedelta | int | None) – should be a number of seconds, or `None` (default) if the cookie should last only as long as the client’s browser session. Additionally `timedelta` objects are accepted, too.

    - expires (str | datetime | int | float | None) – should be a `datetime` object or unix timestamp.

    - path (str | None) – limits the cookie to a given path, per default it will span the whole domain.

    - domain (str | None) – Use this if you want to set a cross-domain cookie. For example, `domain="example.com"` will set a cookie that is readable by the domain `www.example.com`, `foo.example.com` etc. Otherwise, a cookie will only be readable by the domain that set it.

    - secure (bool) – The cookie will only be available via HTTPS

    - httponly (bool) – disallow JavaScript to access the cookie. This is an extension to the cookie standard and probably not supported by all browsers.

    - charset – the encoding for string values.

    - sync_expires (bool) – automatically set expires if max_age is defined but expires not.

    - max_size (int) – Warn if the final header value exceeds this size. The default, 4093, should be safely supported by most browsers. Set to 0 to disable this check.

    - samesite (str | None) – Limits the scope of the cookie such that it will only be attached to requests if those requests are same-site.

    - partitioned (bool) – Opts the cookie into partitioned storage. This will also set secure to True

    - key (str)

    - value (str)

  Return type:

    str

  Changed in version 3.1: The `partitioned` parameter was added.

  Changelog

  Changed in version 3.0: Passing bytes, and the `charset` parameter, were removed.

  Changed in version 2.3.3: The `path` parameter is `/` by default.

  Changed in version 2.3.1: The value allows more characters without quoting.

  Changed in version 2.3: `localhost` and other names without a dot are allowed for the domain. A leading dot is ignored.

  Changed in version 2.3: The `path` parameter is `None` by default.

  Changed in version 1.0.0: The string `'None'` is accepted for `samesite`.

## Conditional Response Helpers

For conditional responses the following functions might be useful:

werkzeug.http.parse_etags(value)

  Parse an etag header.

  Parameters:

    value (str | None) – the tag header to parse

  Returns:

    an `ETags` object.

  Return type:

    ETags

werkzeug.http.quote_etag(etag, weak=False)

  Quote an etag.

  Parameters:

    - etag (str) – the etag to quote.

    - weak (bool) – set to `True` to tag it “weak”.

  Return type:

    str

werkzeug.http.unquote_etag(etag: str) → tuple[str, bool]
werkzeug.http.unquote_etag(etag: None) → tuple[None, None]

  Unquote a single etag:

      >>> unquote_etag('W/"bar"')
      ('bar', True)
      >>> unquote_etag('"bar"')
      ('bar', False)

  Parameters:

    etag (str | None) – the etag identifier to unquote.

  Returns:

    a `(etag, weak)` tuple.

  Return type:

    tuple[str, bool] | tuple[None, None]

werkzeug.http.generate_etag(data)

  Generate an etag for some data.

  Changelog

  Changed in version 2.0: Use SHA-1. MD5 may not be available in some environments.

  Parameters:

    data (bytes)

  Return type:

    str

werkzeug.http.is_resource_modified(environ, etag=None, data=None, last_modified=None, ignore_if_range=True)

  Convenience method for conditional requests.

  Parameters:

    - environ (WSGIEnvironment) – the WSGI environment of the request to be checked.

    - etag (str | None) – the etag for the response for comparison.

    - data (bytes | None) – or alternatively the data of the response to automatically generate an etag using `generate_etag()`.

    - last_modified (datetime | str | None) – an optional date of the last modification.

    - ignore_if_range (bool) – If `False`, `If-Range` header will be taken into account.

  Returns:

    `True` if the resource was modified, otherwise `False`.

  Return type:

    bool

  Changelog

  Changed in version 2.0: SHA-1 is used to generate an etag value for the data. MD5 may not be available in some environments.

  Changed in version 1.0.0: The check is run for methods other than `GET` and `HEAD`.

## Constants

werkzeug.http.HTTP_STATUS_CODES

  A dict of status code -> default status message pairs. This is used by the wrappers and other places where an integer status code is expanded to a string throughout Werkzeug.

## Form Data Parsing

Werkzeug provides the form parsing functions separately from the request object so that you can access form data from a plain WSGI environment.

The following formats are currently supported by the form data parser:

- `application/x-www-form-urlencoded`

- `multipart/form-data`

Nested multipart is not currently supported (Werkzeug 0.9), but it isn’t used by any of the modern web browsers.

Usage example:

    >>> from io import BytesIO
    >>> from werkzeug.formparser import parse_form_data
    >>> data = (
    ...     b'--foo\r\nContent-Disposition: form-data; name="test"\r\n'
    ...     b"\r\nHello World!\r\n--foo--"
    ... )
    >>> environ = {
    ...     "wsgi.input": BytesIO(data),
    ...     "CONTENT_LENGTH": str(len(data)),
    ...     "CONTENT_TYPE": "multipart/form-data; boundary=foo",
    ...     "REQUEST_METHOD": "POST",
    ... }
    >>> stream, form, files = parse_form_data(environ)
    >>> stream.read()
    b''
    >>> form['test']
    'Hello World!'
    >>> not files
    True

Normally the WSGI environment is provided by the WSGI gateway with the incoming data as part of it. If you want to generate such fake-WSGI environments for unittesting you might want to use the `create_environ()` function or the `EnvironBuilder` instead.

class werkzeug.formparser.FormDataParser(stream_factory=None, max_form_memory_size=None, max_content_length=None, cls=None, silent=True, *, max_form_parts=None)

  This class implements parsing of form data for Werkzeug. By itself it can parse multipart and url encoded form data. It can be subclassed and extended but for most mimetypes it is a better idea to use the untouched stream and expose it as separate attributes on a request object.

  Parameters:

    - stream_factory (TStreamFactory | None) – An optional callable that returns a new read and writeable file descriptor. This callable works the same as `Response._get_file_stream()`.

    - max_form_memory_size (int | None) – the maximum number of bytes to be accepted for in-memory stored form data. If the data exceeds the value specified an `RequestEntityTooLarge` exception is raised.

    - max_content_length (int | None) – If this is provided and the transmitted data is longer than this value an `RequestEntityTooLarge` exception is raised.

    - cls (type[MultiDict[str, t.Any]] | None) – an optional dict class to use. If this is not specified or `None` the default `MultiDict` is used.

    - silent (bool) – If set to False parsing errors will not be caught.

    - max_form_parts (int | None) – The maximum number of multipart parts to be parsed. If this is exceeded, a `RequestEntityTooLarge` exception is raised.

  Changelog

  Changed in version 3.0: The `charset` and `errors` parameters were removed.

  Changed in version 3.0: The `parse_functions` attribute and `get_parse_func` methods were removed.

  Changed in version 2.2.3: Added the `max_form_parts` parameter.

  Added in version 0.8.

werkzeug.formparser.parse_form_data(environ, stream_factory=None, max_form_memory_size=None, max_content_length=None, cls=None, silent=True, *, max_form_parts=None)

  Parse the form data in the environ and return it as tuple in the form `(stream, form, files)`. You should only call this method if the transport method is `POST`, `PUT`, or `PATCH`.

  If the mimetype of the data transmitted is `multipart/form-data` the files multidict will be filled with `FileStorage` objects. If the mimetype is unknown the input stream is wrapped and returned as first argument, else the stream is empty.

  This is a shortcut for the common usage of `FormDataParser`.

  Parameters:

    - environ (WSGIEnvironment) – the WSGI environment to be used for parsing.

    - stream_factory (TStreamFactory | None) – An optional callable that returns a new read and writeable file descriptor. This callable works the same as `Response._get_file_stream()`.

    - max_form_memory_size (int | None) – the maximum number of bytes to be accepted for in-memory stored form data. If the data exceeds the value specified an `RequestEntityTooLarge` exception is raised.

    - max_content_length (int | None) – If this is provided and the transmitted data is longer than this value an `RequestEntityTooLarge` exception is raised.

    - cls (type[MultiDict[str, t.Any]] | None) – an optional dict class to use. If this is not specified or `None` the default `MultiDict` is used.

    - silent (bool) – If set to False parsing errors will not be caught.

    - max_form_parts (int | None) – The maximum number of multipart parts to be parsed. If this is exceeded, a `RequestEntityTooLarge` exception is raised.

  Returns:

    A tuple in the form `(stream, form, files)`.

  Return type:

    t_parse_result

  Changelog

  Changed in version 3.0: The `charset` and `errors` parameters were removed.

  Changed in version 2.3: Added the `max_form_parts` parameter.

  Added in version 0.5.1: Added the `silent` parameter.

  Added in version 0.5: Added the `max_form_memory_size`, `max_content_length`, and `cls` parameters.